The overall goal of the three projects in this IRPG is to develop effective monoclonal antibody-based strategies for treatment of breast cancer. The project described here will initiate clinical trials of humanized forms of breast epithelial-directed antibodies. Two such antibodies have been developed and tested in the murine forms in clinical trials by this group; the tumor localization and pharmacokinetics of one, BrE-3, suggest therapeutic potential. However, murine antibodies are limited in their application by their immunogenicity. Humanization, which has been accomplished already for BrE-3, should overcome the limitation of immunogenicity. Humanization thus may permit therapeutic strategies based on dose fractionation which may be expected to increase the therapeutic index. The clinical project described here will test these hypotheses. In addition, this project will interact with the other projects in the IRPG in the design and testing of additional humanized antibodies, directed against different breast epithelial antigens, and in the identification of the immunogenic sites in the humanized antibodies. Through the use of antibody cocktails or alternating cycles of antibodies against different epitopes, we hope to circumvent development of anti-idiotypic responses, to further improve tumor targeting, and increase therapeutic index. The studies will be carried out under the following specific aims: 1)To determine the localization and pharmacokinetic parameters of a humanized monoclonal antibody, specifically, (111)In-MX-DTPA humanized BrE-3 reactive against a 400kD epitope of breast epithelial mucin, and to characterize its immunogenicity in patients. 2) To measure the same parameters for (111)In-MX-DTPA Mc3 which reacts with a different breast epithelial antigen. 3) To test dose fractionation radioimmunotherapy regimens using two different humanized antibodies. The availability of a second, alternative antibody is expected to help circumvent the anti- idiotypic response which occurs and to increase therapeutic index. These studies will provide the first clinical results of humanized forms of breast epithelial directed antibodies and could form the basis for the further development of successful strategies for radioimmunotherapy in breast cancer.